1. Field of the Invention
The present invention relates to a toner which is applied to and visualize a latent electrostatic image formed on a photoconductor in electrophotography and electrostatic recording or the like, and to a developer using the toner, a toner container, a process cartridge containing the toner, an image-forming process using the toner and an image-forming apparatus using the toner.
2. Description of the Related Art
In the prior art, an electrical or magnetic latent image formed with an electrophotography apparatus or electrostatic recording apparatus is visualized using a toner. For example, in the electrophotography method, an electrostatically charged image (latent image) is formed on a photoconductor, and this latent image is then developed using a toner to form a toner image (electrostatic charge image development). This toner image is usually transferred to a transfer medium such as paper, and subsequently fixed by a method such as heating.
In general, the toner used for the electrostatic charge image development comprises coloring particles containing a colorant, charge control agent and other additives in a binder resin, and may be manufactured, broadly speaking, by a pulverization method or a suspension-polymerization method. In the pulverization method, a toner is manufactured by melt-mixing the colorant, charge control agent and offset inhibitor, uniformly dispersing them in a thermoplastic resin, and then pulverizing and classifying the composition obtained. By the pulverization method, a toner having excellent characteristics can be manufactured, but selection of toner materials is limited. For example, the composition obtained by melt mixing must be a material which can be pulverized and classified by an economically viable apparatus. Due to this requirement, the composition which is melt-mixed must be sufficiently brittle to be pulverized and classified. Thus, when the composition is actually pulverized to particles, a particle size distribution tends to be widely ranged, and if it is attempted to obtain a copy image with good resolution and gradation, fines with a particle size of for example 5 μm or less and coarse powder of 20 μm or more must be removed, so the yield becomes very low. Moreover, it is difficult to disperse a colorant and charge control agent uniformly in a thermoplastic resin by the pulverization method. Uneven dispersion of the components has an adverse effect on toner fluidity, development and durability, and image quality.
Recently, to overcome the problems in these pulverization methods, it was proposed to manufacture the toner by a suspension-polymerization method, and this method is now being used. The technology of manufacturing a toner for latent electrostatic image development by polymerization, for example obtaining toner particles by a suspension-polymerization method, is known in the art. However, the toner particles obtained by the suspension-polymerization method are spherical, and they are not easy to clean off. In developing/transfer, when the occupation ratio of the image area is low, there is a little residual toner and poor cleaning does not pose a problem. However, when the occupation ratio of the image area is high, such as in a photographic image, toner which is not transferred after image-forming may lead to toner transfer residues on the photoconductor, and if this accumulates, a toner deposition may occur on the background of the image. Further, toner which is not transferred may contaminate the charge roller which contact charges the photoconductor, so that in some cases it cannot exhibit its original charging capability. These disadvantages become more serious if paper feed is unsatisfactory.
In order to solve these problems, a method has been disclosed for making the resin particles obtained by emulsion-polymerization aggregate so as to obtain toner particles of irregular shape (Japanese Patent Application Publication (JP-B) No. 2537503).
However, even if the toner particles obtained by emulsion-polymerization are subjected to a water rinsing step, as surfactant remains not only on the surface but also in the interior of the particles, the environmental stability of the toner charge is adversely impacted, the charge distribution is broadened, and the obtained image is soiled. Moreover, the remaining surfactant also contaminates the photoconductor, charge roller and developing roller, so that they are not able to manifest their original charging capability.
In the fixing step of the contact heating method using heating members such as a heat roller, a releasing quality (hereafter, “anti-offset quality”) of the toner particles relative to the heating member is required. This anti-offset quality can be enhanced by introducing a releasing agent into the toner particle surface. Japanese Patent Application Laid-open (JP-A) No. 2000-292973 and JP-A No. 2000-292978 disclose a method of improving anti-offset quality not only by incorporating fine resin particles in the toner particles, but also by unevenly dispersing these fine resin particles on the toner particle surface. However, in these methods, the minimum fixing temperature rises, and the low-temperature fixing quality, i.e., energy-saving fixing quality, is not sufficient.
The following problems are also caused when the resin particles obtained by emulsion-polymerization are made to aggregate so as to obtain toner particles of irregular shape.
Firstly, when making releasing agent particles aggregate to improve the anti-offset quality, these releasing agent particles are taken into the interior of the toner particles, and as a result, a full improvement of the anti-offset quality cannot be realized. Secondly, as the fine resin particles, releasing agent particles and colorant particles stick together randomly to form the toner particles, variations occur in the composition (component proportions) of the toner particles, and scatter occurs in the molecular weight of the component resin. As a result, the toner particles have different surface characteristics, and an image which is stable over a long period of time cannot be formed. Thirdly, in low-temperature fixing systems wherein low-temperature fixing is required, fixing is inhibited by the resin particles which are unevenly dispersed on the toner surface, and the fixing temperature width cannot be ensured.
In order to solve these problems, JP-A No. 2002-169336 discloses a method of obtaining irregular toner particles by dissolving or dispersing a toner composition containing a toner binder resin (i) comprising a modified polyester resin capable of reacting with compounds having active hydrogen groups in an organic solvent, dispersing this solution or dispersion in an aqueous medium comprising fine resin particles, reacting this with a compound having an active hydrogen group, and then removing the solvent from the dispersion obtained so as to obtain irregular toner particles. However, in this method, if this crosslinking or elongation reaction is inadequate, new problems arise, i.e., the obtained toner particles acquire a strong positive electrostatic charge, the environmental stability of the negative toner charge is lost, the charging amount distribution is broadened, and the obtained image is badly soiled.
Advantages and Objects
It is therefore a first object of the present invention to provide a toner which gives a sharp negative electrostatic toner charging distribution, and which can form good, clear, visible images over a long period of time.
It is a second object of the present invention to provide a toner which is always easy to clean, is suitable for low-temperature fixing systems, has good anti-offset qualities, and does not soil the fixing apparatus and image.
It is a third object of the present invention to provide a developer containing the aforesaid toner, a process cartridge, image-forming process and image-forming apparatus using this toner, and a toner container filled with the developer containing this toner.